(a) Field of the Invention
The present invention relates to an electrostatic discharge diode for protecting a semiconductor circuit from static electricity or stress input to the semiconductor circuit.
(b) Description of the Related Art
An electrostatic discharge diode (hereafter, ESD) of a prior semiconductor circuit has one trigger voltage for electrostatic discharge clamping. That is, when a voltage generated by static electricity (hereafter called “electrostatic voltage”) is larger than the trigger voltage, the electrostatic discharge diode is turned on and the electrostatic voltage is discharged. Then, the electrostatic voltage input to the semiconductor circuit is not larger than the trigger voltage and electrostatic voltage is clamped as the trigger voltage. Accordingly, for protecting the semiconductor circuit, a low voltage diode having a low trigger voltage can be used. When a high voltage diode having a high trigger voltage is used, the semiconductor circuit can be damaged before the electrostatic voltage reaches the trigger voltage. Since the low voltage diode has a high dopant concentration, an electrostatic discharge threshold voltage is low and the low voltage diode is suitable for discharging the electrostatic voltage. However, in the low voltage diode, when an electrical surge occurs, since a sustaining voltage of the low voltage diode is very low, a dielectric breakdown of the semiconductor circuit can occur because of the electrical surge. A sustaining voltage is a voltage difference applied between an anode and a cathode of a diode just before the diode is destroyed by the electrical surge. On the other hand, since the high voltage diode has a low dopant concentration, an electrostatic discharge threshold voltage is rather high and the diode is not suitable for discharging the electrostatic voltage. However, in the high voltage diode, when an electrical surge occurs, since the sustaining voltage of the high voltage diode is high, a dielectric breakdown of the semiconductor circuit by an electrical surge can be prevented. As stated above, there are problems that the high concentration dopant diode is weak to an electrical surge and the low concentration dopant diode is not suitable for discharging the electrostatic voltage. The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.